Well, I'll go straight to the point:
How about a signature size limit?

Overgrown signatures lately become very annnoying. It's just absurd, seeing posts containing no more than 10 words and a half-screen signature under it. Big pictures are not the only problem here, massive text signatures are even a bigger issue- they can't be blocked by ad-blocks. Come on, it is SIGNATURE, not an essay- nobody reads those.

So my suggestions are:
1) Create a limit for letters in signature. 200-400 maybe? It will help people keep it short and sharp, not long and expressionless like toilet paper.
2) Create a pixel size limit for signature images. 100x400? 150px height on width of a post frame? I know it might be tough, especially that forum supports linking to external images. Still, worth trying.
3) Create a kilobyte size limit for signature images. 100-500kb? Some people are still using modem internet, overgrown animated signatures may be a real problem for them.
4) Create an image number limit for signature images. One image? Two images? Four images tops? I know dragoncave is fun but some people just overdo. There are sites like "Eggswillbedragons" after all.

5) It would be also nice to give a topic creator an option to allow or disallow displaying signatures in his topic. If someone's creating a guide for example, or any good knowledge topic it needs to stay as clean and watchable as it can be. Disallowing signatures could help achieving it.

6) Last but not least we could use a profile option to show or hide all signatures. It would solve it all, even without limiting signatures. Every user will decide whether he likes or dislikes watching sigs.